ValueAspectPropertyValueModelAdapter.java

/*******************************************************************************
 * Copyright (c) 1998, 2015 Oracle and/or its affiliates. All rights reserved.
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v1.0 and Eclipse Distribution License v. 1.0
 * which accompanies this distribution.
 * The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v10.html
 * and the Eclipse Distribution License is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * Contributors:
 *     Oracle - initial API and implementation from Oracle TopLink
******************************************************************************/
package org.eclipse.persistence.tools.workbench.uitools.app;

import java.beans.PropertyChangeEvent;

/**
 * Abstract property value model that provides behavior for wrapping a property
 * value model and listening for changes to aspects of the *value* contained
 * by the value model. Changes to the actual value are also monitored.
 *
 * This is useful if you have a value that may change, but whose aspects can also
 * change in a fashion that might change the value's external appearance.
 *
 * Subclasses need to override two methods:
 *
 * listenToValue(Model)
 *     begin listening to the appropriate aspect of the specified value and call
 *     #valueAspectChanged(Object) whenever the aspect changes
 *
 * stopListeningToValue(Model)
 *     stop listening to the appropriate aspect of the specified value
 */
public abstract class ValueAspectPropertyValueModelAdapter
    extends PropertyValueModelWrapper
{
    /** Cache the value so we can disengage. */
    protected Object value;


    // ********** constructor **********

    /**
     * Constructor - the value holder is required.
     */
    protected ValueAspectPropertyValueModelAdapter(PropertyValueModel valueHolder) {
        super(valueHolder);
    }


    // ********** initialization **********

    protected void initialize() {
        super.initialize();
        this.value = null;
    }


    // ********** ValueModel implementation **********

    /**
     * @see ValueModel#getValue()
     */
    public Object getValue() {
        return this.value;
    }


    // ********** PropertyValueModel implementation **********

    /**
     * @see PropertyValueModel#setValue(Object)
     */
    public void setValue(Object value) {
        this.valueHolder.setValue(value);
    }


    // ********** PropertyValueModelWrapper implementation **********

    /**
     * @see PropertyValueModelWrapper#valueChanged(java.beans.PropertyChangeEvent)
     */
    protected void valueChanged(PropertyChangeEvent e) {
        this.disengageValue();
        this.engageValue();
        this.firePropertyChanged(e.getPropertyName(), e.getOldValue(), e.getNewValue());
    }


    // ********** behavior **********

    /**
     * Start listening to the value holder and the value.
     */
    protected void engageValueHolder() {
        super.engageValueHolder();
        this.engageValue();
    }

    protected void engageValue() {
        this.value = this.valueHolder.getValue();
        if (this.value != null) {
            this.startListeningToValue();
        }
    }

    /**
     * Start listening to the current value.
     * At this point we can be sure that the value is not null.
     */
    protected abstract void startListeningToValue();

    /**
     * Stop listening to the value holder and the value.
     */
    protected void disengageValueHolder() {
        this.disengageValue();
        super.disengageValueHolder();
    }

    protected void disengageValue() {
        if (this.value != null) {
            this.stopListeningToValue();
            this.value = null;
        }
    }

    /**
     * Stop listening to the current value.
     * At this point we can be sure that the value is not null.
     */
    protected abstract void stopListeningToValue();

    protected void valueAspectChanged() {
        this.firePropertyChanged(VALUE, this.value);        // hmmm...
    }

}